The present invention relates, in general, to high strength corrosion resistant alloys, and, in particular, to a new and useful austenitic alloy containing critical amounts of nickel, chromium, silicon, copper, molybdenum and manganese, with iron and incidental impurities.
The need for a high strength and corrosion resistant alloy that will retain its integrity in the hostile environment of deep oil sour wells, has become apparent with the decrease of easily obtained sweet oil reserves. Since sour wells can contain significant amounts of hydrogen sulfide, carbon dioxide, and chloride solutions at high temperatures and pressures, alloys with better resistance to failure under stress and corrosive conditions would be desirable.
To minimize corrosion, various high alloy stainless steels and nickel alloys are now being used for other applications. Some disadvantages with most of these alloys have been, however, the relatively high cost because of the increased alloying content, relatively complicated manufacturing, and the fact that these alloys are still subject to stress corrosion cracking. Many metalurgical factors influence the mechanical and corrosion behavior of these alloys. These factors include microstructure, composition, and strength. All of these factors are interrelated and must be closely controlled or optimized with respect to sour well applications.
U.S. Pat. Nos. 4,400,209; 4,400,210; 4,400,211; 4,400,349; and 4,421,571, all to Kudo et al, disclose high strength alloys which are particularly useful for deep well casing, tubing and drill pipes, and which utilize compositions including nickel, chromium, manganese and molybdenum. These patents also rely on tungsten additions that satisfies a specific relationship with the presence of chromium and molybdenum to make up a significant proportion of the alloy as a whole.
U.S. Pat. No. 4,489,040 to Asphahani et al, also discloses a corrosion resistant alloy including nickel and chromium plus tungsten.
Titanium is also utilized as an additive for corrosion resistant nickel-chromium alloys as disclosed in U.S. Pat. Nos. 4,409,025 and 4,419,129 to Sugitani et al, and U.S. Pat. No. 4,385,933 to Ehrlich et al.
Niobium is an additive for corrosion resistant alloys as disclosed by U.S. Pat. No. 4,505,232 to Usami et al, U.S. Pat. No. 4,487,744 to DeBold et al, and U.S. Pat. No. 4,444,589 to Sugitani et al.
An oxidation resistant austenitic steel advocating relatively low chromium and nickel contents is disclosed by U.S. Pat. No. 4,530,720 to Moroishi et al.
Lanthanum can be an additive for austenitic stainless steel as disclosed by U.S. Pat. No. 4,421,557 to Rossomme et al.
As evidenced by several of the foregoing reference which include relatively high chromium contents, the presence of nitrogen is desireable. Nitrogen additions is used in some alloys to replace chromium for maintaining a stable austenitic structure. Chromium normally exists in the ferritic form.